The deceased have been identified as Vijay (16), Vivek (15) and Arjun (12), they said.
A senior police officer said divers rescued another teenager Vijay Rathore (17) and was rushed to a hospital.
The boys came to the river from Sonia Vihar Pusta number 2 side for idol immersion. There was a heavy flow on that side and they drowned. Divers tried to find the bodies after the incident, but it was dark and the operation had to be suspended, he said.
The rescue operation continued on Sunday but the three bodies are yet to be found, the officer said.
Fire officials said the rescue efforts are being carried out by the NDRF, fire personnel and local divers.
The three boys are residents of Ankur Enclave in Karawal Nagar, police said.
The families of the boys were informed about the incident and they immediately reached the spot, the police said.
In another incident, a 29-year-old man died after he fell into a drain in a waterlogged area in north Delhi’s Narela.
The deceased has been was identified as Salesh Mehto, a labourer at DSIDC. His body was pulled out and taken to a hospital where he was declared brought dead, police said.
The incident took place on Saturday in Delhi State Industrial and Infrastructure Development Corporation Ltd (DSIDC) area, they said.
Due to the heavy rains, there was waterlogging in the area. He accidently fell into a drain, police said.
Mehto was a native of Chapra in Bihar, they said.